Donald Trump was the big winner Tuesday night

For all of Donald Trump's struggles in his first 19 months as President, there's one thing he's proven particularly adept at: Picking winners in contested GOP primaries.

That run of winners continued Tuesday night when voters went to the polls in Arizona and Florida.

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The most obvious example of Trump's power within the party is in the Florida governor's race, where, late last year, he tweeted favorably about the candidacy of Rep. Ron DeSantis, who was seen as a heavy underdog to state Agriculture Commissioner Adam Putnam in the primary.

"Congressman Ron DeSantis is a brilliant young leader, Yale and then Harvard Law, who would make a GREAT Governor of Florida," Trump tweeted just days before Christmas. "He loves our Country and is a true FIGHTER!"

DeSantis cruised to victory. "Such a fantastic win for Ron DeSantis and the people of the Great State of Florida," tweeted Trump. "Ron will be a fantastic Governor. On to November!"

In Arizona's Senate primary, Republican strategists long worried that Rep. Martha McSally, a moderate who polling suggests is the party's best chance to hold the seat, would lose if Trump came out and endorsed either one of her more Trumpian opponents: Former state legislator Kelli Ward, or pardoned Maricopa County Sheriff Joe Arpaio.

Those same strategists were beyond thrilled when, at a ceremony signing the defense authorization bill in New York, Trump said this of McSally: "I've gotten to know her very well, and she is terrific."

That quasi-endorsement may well have sealed McSally's victory. She won convincingly on Tuesday night -- and Trump quickly moved to take credit -- and take a shot at the man McSally is running to replace. "Martha McSally, running in the Arizona Primary for U.S. Senate, was endorsed by rejected Senator Jeff Flake....and turned it down - a first!," tweeted Trump. "Now Martha, a great U.S. Military fighter jet pilot and highly respected member of Congress, WINS BIG. Congratulations, and on to November!"

The Point: Trump says lot of things that stretch the truth. But one thing he's absolutely right about is his popularity among Republican voters. Victories by DeSantis and McSally simply (re)prove that reality.